1. Field of the Invention
This invention relates to laminates, and more particularly, to laminates having thermal insulation and optionally vibration damping properties, and to assemblies and structures incorporating the laminates.
2. Description of the Related Art
Laminates comprising outer and inner metal skin layers with an interposed insulation material have been used to provide thermal insulation and vibration and noise control in a variety of applications. The insulation material typically has been selected from ceramic, glass cloth, and asbestos.
Many of the laminates having this conventional construction suffered because the insulation layers were not weldable to the skins or the entire laminates were not weldable to other structures. These drawbacks limit the flexibility of the use of the laminates with other structures and the ability to form the laminates into finished products, such as tubing. The insulation layer selected for the laminates also did not have structural integrity, further limiting the usefulness of the laminates.
Many of these problems have been largely overcome by U.S. Pat. No. 6,465,110 to Boss et al., the disclosure of which is incorporated herein by reference, the assignee of which is the assignee hereof, which discloses in certain embodiments a laminate having vibration damping and thermal insulation properties. An embodiment of a laminate disclosed in Boss has been reproduced herein and is designated by reference numeral 1020 in FIGS. 11 and 12. The laminate 1020 comprises a first imperforate metal layer 1022 having an interior surface 1026 and an exterior surface 1030, and a second imperforate metal layer 1024 having an interior surface 1028 and an exterior surface 1032. A first adhesive layer 1034 is formed on the interior surface 1026 of the first imperforate metal layer 1022. A second adhesive layer 1036 is formed on the interior surface 1028 of the second imperforate metal layer 1024. Sandwiched between the metal layers 1022 and attached to the adhesive layers 1034 and 1036 is a metallic felt layer 1038.
The laminate 1020 is shapeable into a substantially cylindrical structure by rolling the laminate 100 to bring its opposite side edge portions into end-to-end abutting relationship. One drawback of forming the laminate 1020 into a cylindrical structure is the degree of precision involved in placing the side edge portions in abutting relationship while controlling the inner and outer diameters of the resulting cylindrical structure. This drawback of precisely fitting the laminate edge portions in end-to-end abutting relationship may be largely overcome by placing the side edge portions in overlapping relationship with one another. FIGS. 13A and 13B illustrate the laminate 1020 (without optional adhesive layers 1034 and 1036) as the laminate 1020 might appear if shaped around a cylindrical pipe 1045 to bring the opposite side edge portions of the laminate 1020 into overlapping relationship. However, the arrangement of the opposite side edge portions in overlapping relationship may adversely impact the ability of the tubular laminate 1020 to function as a thermal barrier between the cylindrical exhaust pipe 1045, which carries hot exhaust gases, and the outside environment. The thermal insulating properties of the laminate 1020 are derived primarily from the metallic felt layer 1038. The first and second metal layers 1022 and 1024, on the other hand, are relatively thermally conductive compared to the metallic felt layer 1038. Overlapping the opposite side edge portions allows the inner second metal layer 1024 to physically contact and thermally communicate with the outer first metal layer 1022. As represented by the arrows in FIG. 13B, the contacting metal layers 1022 and 1024 form a thermally conductive metallic path leading from the cylindrical pipe 1045 to the outside environment. As a consequence, thermal energy is permitted to pass from the inner second metal layer 1024, which is heated by the adjacent exhaust pipe 1045, to the outer first metal layer 1022 at the overlapping region, thereby elevating the temperature of the outer first metal layer 1022 and permitting the escape of heat past the metallic felt layer 1038.